code 41507;
real procedure CHISQINV(PROB, DF);
    value PROB, DF; real PROB, DF;
if PROB < 10-10 ∨ PROB > 1 - 10-10
then STATAL3 ERROR(“CHISQINV”, 1, PROB)
else if DF ≤ 0
then STATAL3 ERROR(“CHISQINV”, 2, DF)
else
begin real X;
    X:= PHINV(PROB) × SQRT(2 × DF) + DF;
    CHISQINV:= INVERSE(X, CHISQ(X, DF), PROB, 10-10)
end CHISQINV;
eop